Hydrothermal vent community zonation along environmental gradients at the Lau back-arc spreading center,

Description

The Lau back-arc spreading center exhibits gradients in hydrothermal vent habitat characteristics from north to south. Biological zonation within a few meters of vents has been described as temperature driven. We constructed georeferenced photomosaics of the seafloor out to tens of meters beyond vents to describe peripheral zonation and explore correlations between environmental conditions and the biological community. Cluster analysis separated northern sites from southern sites, corresponding to a break in substrate from basalt in the north to andesite in the south. Northern sites were dominated by anemones, and southern by sponges. A previous suggestion that dominants may be dependent on friability of the substrate was not supported; when visually distinguishable, individual species within taxa showed different patterns. Northern sites hosted proportionally more suspension feeding species. Sulfide that can support microbial food sources is at higher concentrations at these sites, though bathymetry that may enhance bottom currents is less rugged. Northern sites had higher diversity that may result from the overall northwards flow, which would generally permit easier dispersal downcurrent, though we observed no difference in dispersal strategies at different sites., Cited By (since 1996):1, CODEN: DRORE, ,

Determination of the water-leaving spectral radiance using in-water instrumentation requires measurements of the upwelling spectral radiance (L u) at several depths. If these measurements are separated in time, changes in the measurement conditions result in increased variance in the results. A prototype simultaneous multi-track system was developed to assess the potential reduction in the Type A uncertainty in single set, normalized water-leaving radiance achievable if the data were acquired simultaneously. The prototype system employed a spectrograph and multi-track fiber-coupled CCD-detector; in situ in-water tests were performed with the prototype system fiber-coupled to a small buoy. The experiments demonstrate the utility of multi-channel simultaneous data acquisition for in-water measurement applications. An example of the potential impact for tracking abrupt responsivity changes in satellite ocean color sensors using these types of instruments as well as for the satellite vicarious calibration is given., Cited By (since 1996):1, Oceanography, Art. No.: 66800J, CODEN: PSISD, ,

Development of the ROV SCINI and deployment in McMurdo Sound, Antarctica

Description

Remotely Operated Vehicles (ROVs) are powerful tools whose use has become common in many aquatic systems, for many purposes, from commercial to research applications. Polar regions, because of ice cover and harsh conditions, remain difficult locations for ROV work. This paper outlines the development of an ROV designed to facilitate exploration and scientific research under sea ice, giving easier access to largely unexplored regions of the seafloor. The ROV SCINI (Submersible Capable of under Ice Navigation and Imaging) was developed at Moss Landing Marine Laboratories and deployed in Antarctica for four field seasons, from 2007 to 2011. Ice provides a convenient deployment platform but commercially available ROVs require a large hole in the ice and much logistic support, which restricts their use in polar regions. Unlike other ROVs, SCINI has a slender torpedo shape (length: 1.4 m, diameter: 15 cm), which allows it to be deployed through a 20 cm hole in the ice. This small hole can be drilled by two people, using a handheld drill. The entire SCINI system and personnel (three or more persons) can fit in one helicopter, thus giving easy and quick access to remote sites. SCINI is a modular vehicle that can easily be modified or serviced in the field. It is also rugged and designed for harsh polar conditions. SCINI is equipped with two video cameras, scaling lasers, and lights. Its maximum depth capability is 300 m. A long baseline acoustic positioning system is used for navigation. SCINI is a highly manoeuvrable vehicle, better suited for flying transects over the seafloor than most ROVs. Engineering tests and scientific surveys were based out of McMurdo Station, Antarctica, and carried out at various sites within a 100 km radius. Knowledge gained from these deployments led to numerous modifications and improvements to the vehicle. This paper provides details on the vehicle's most recent configuration, including mechanical design, electrical design, software, and navigation system. Deployment methods, vehicle behaviour, and results of field testing are described. Four scientific surveys are also briefly described as examples. Copyright Journal of Ocean Technology 2011., Cited By (since 1996):3,
Oceanography

Distribution and near-bottom transport of larvae and other plankton at hydrothermal vents,

Description

Distributions of larvae of benthic invertebrates and other planktonic organisms (holoplankton) were determined near hydrothermal vents along the East Pacific Rise (9°50'N) and combined with current meter records to estimate the extent and direction of transport in near-bottom flows. Diurnal tidal currents were strong enough to transport larvae substantial distances (up to 2 km) across the ridge axis during a single 12-h excursion. Potential longer-term transport in mean flows, however, appeared to be relatively slow (typically less than 1 km d-1). The proportion of larvae dispersing in near-bottom flows, as opposed to becoming entrained into the buoyant plume (and transported up out of the near-bottom environment) was estimated for a range of vent community sizes and black-smoker buoyancy fluxes, using a buoyant-plume entrainment model. These estimates suggested that larvae were most often transported in near-bottom currents, but that plume-level dispersal dominated for short periods of the tidal cycle (0.5-3 h) when the currents were slower than 1-2 cm s-1. The plume exit temperature also affects entrainment rate, so the proportion of larvae in each transport pathway (near-bottom flows and buoyant plumes) should vary substantially among vent habitats surrounding different temperature vents. The presence of certain holoplankton groups in diffuse vent flows, and their elevated abundances within the axial ridge valley, raises the possibility that these groups may be specifically associated with vent habitats., Cited By (since 1996):38, Invertebrates, CODEN: DSROE, ,

Sponges are the most conspicuous component of the Antarctic benthic ecosystem, a system under stress both from climate change and fishing activities. Observations over four decades are compiled and reveal extremely episodic sponge recruitment and growth. Recruitment occurred under different oceanographic conditions on both sides of McMurdo Sound. Most of the sponges appear to have recruited in the late 1990s–2000. Observations from 2000 to 2010 follow thirty years of relative stasis with very little sponge recruitment or growth followed by a general pattern of recruitment by some forty species of sponges. That there was almost no recruitment observed on natural substrata emphasizes the contrast between potential and realized recruitment. This unique data set was derived from a region noted for physical stasis, but the episodic ecological phenomena highlight the importance of rare events. Against a background of intermittent food resources and the low metabolic costs of stasis, understanding the causes of irregular larval supply, dispersal processes, recruitment success and survivorship becomes critical to predicting ecosystem dynamics and resilience in response to increasing environmental change. Our time-series emphasizes that long-term data collection is essential for meaningful forecasts about environmental change in the unique benthic ecosystems of the Antarctic shelf.

Swarming benthic crustaceans in the Bering and Chukchi seas and their relation to geographic patterns in gray whale feeding,

Description

Swarms differed in their geographic extent, local biomass, and life stages of swarming individuals and thus in their availability to feeding Eschrichtius robustus. Immature amphipods apparently swarmed for dispersal, whereas cumaceans probably swarmed for mating. All life stages of the hyperbenthic mysids occurred above the sea floor. Although the geographic spread of mysid swarms and shrimp communities was much greater than for the amphipod and cumacean swarms, the latter swarmed in denser patches to produce higher local biomass. Crustacean swarms are important in describing the geographic patterns of gray whale feeding from the Chukchi Sea to Baja California. The primary feeding ground is in the S Chukchi Sea and especially the N Bering Sea, where gray whales suck infaunal amphipods from fine sand. The primary feeding ground is divided into a relatively deep zone (>20 m), where tube-dwelling ampeliscid amphipods are the major prey, and a shallow zone (<20 m), where burrowing pontoporeid amphipods dominate. The secondary feeding ground is in the S Bering Sea along the E Alaska Peninsula and adjacent Alaskan mainland where shrimp and mysids are the major prey. -from Authors, Cited By (since 1996):16, Invertebrates,
Marine Mammals, Birds & Turtles, ,

Variation in the biomass density and demography of Antarctic krill in the vicinity of the South Shetland Islands during the 1999/2000 austral summer,

Description

Vessels from Japan, Peru, and the USA conducted four sequential surveys designed to estimate the biomass density and demography of Antarctic krill in the vicinity of the South Shetland Islands between late December 1999 and early March 2000. The surveys were conducted during the same austral summer as the CCAMLR 2000 Survey in the Scotia Sea (Watkins et al., Deep-Sea Research, II, this issue [doi: 10.1016/j.dsr2.2004.06.010]), and the data were analyzed in a similar manner. Biomass densities were not significantly different between the surveys and averaged 49 g m -2. Maps of krill biomass indicate three areas of consistently high density: one near the eastern end of Elephant Island, one mid-way between Elephant Island and King George Island, and one near Cape Shirreff on the north side of Livingston Island. The areas of highest krill density appeared to move closer to the shelf break as the season progressed. This apparent movement was accompanied by a change in the demographic structure of the population, with smaller krill absent and a larger proportion of sexually mature animals present in late summer., Cited By (since 1996):8, CODEN: DSROE, Antarctica, ,

High species density patterns in macrofaunal invertebrate communities in the marine benthos,

Description

Species density of macrofaunal invertebrates living in marine soft sediments was highest at the shelf-slope break (100-150m) in Monterey Bay (449 m-2). There were 337 species m-2 in the mid-shelf mud zone (80 m). There were fewer species along the slope: 205 m-2 from the lower slope (950-2000 m) and 335 m-2 on the upper slope (250-750 m). Species density was highest inside the bay (328-446 m-2) compared to outside (336-339 m-2), when examining samples at selected water depths (60-1000 m). There was little difference in local species density from 1 km of shoreline compared to regional species density along 1000 km of shoreline at both shelf and slope depths. The highest species densities worldwide in the literature are recorded along the Carolina slope in the Atlantic Ocean, where peak species density (436/0.81 m2) at 800 m and values at the largest sample areas are similar to those on the Monterey Bay shelf. We speculate that the highest species densities occur where ocean water exchanges energy with shoaling topography at the continental margin, bringing more food to the benthos -- areas such as the very productive waters in the upwelling system of Monterey Bay., Cited By (since 1996):1, ,

Western Pacific hydrothermal vents will soon be subjected to deep-sea mining and peripheral sites are considered the most practical targets. The limited information on community dynamics and temporal change in these communities makes it difficult to anticipate the impact of mining activities and recovery trajectories. We studied community composition of peripheral communities along a cline in hydrothermal chemistry on the Eastern Lau Spreading Center and Valu Fa Ridge (ELSC-VFR) and also studied patterns of temporal change. Peripheral communities located in the northern vent fields of the ELSC-VFR are significantly different from those in the southern vent fields. Higher abundances of zoanthids and anemones were found in northern peripheral sites and the symbiont-containing mussel Bathymodiolus brevior, brisingid seastars and polynoids were only present in the northern peripheral sites. By contrast, certain faunal groups were seen only in the southern peripheral sites, such as lollipop sponges, pycnogonids and ophiuroids. Taxonomic richness of the peripheral communities was similar to that of active vent communities, due to the presence of non-vent endemic species that balanced the absence of species found in areas of active venting. The communities present at waning active sites resemble those of peripheral sites, indicating that peripheral species can colonize previously active vent sites in addition to settling in the periphery of areas of venting. Growth and mortality were observed in a number of the normally slow-growing cladorhizid stick sponges, indicating that these animals may exhibit life history strategies in the vicinity of vents that differ from those previously recorded. A novel facultative association between polynoids and anemones is proposed based on their correlated distributions., Accepted

Results in coastal waters with high resolution in situ spectral radiometry: The Marine Optical System ROV,

Description

The water-leaving spectral radiance is a basic ocean color remote sensing parameters required for the vicarious calibration. Determination of water-leaving spectral radiance using in-water radiometry requires measurements of the upwelling spectral radiance at several depths. The Marine Optical System (MOS) Remotely Operated Vehicle (ROV) is a portable, fiber-coupled, high-resolution spectroradiometer system with spectral coverage from 340 nm to 960 nm. MOS was developed at the same time as the Marine Optical Buoy (MOBY) spectrometer system and is optically identical except that it is configured as a profiling instrument. Concerns with instrument self-shadowing because of the large exterior dimensions of the MOS underwater housing led to adapting MOS and ROV technology. This system provides for measurement of the near-surface upwelled spectral radiance while minimizing the effects of shadowing. A major advantage of this configuration is that the ROV provides the capability to acquire measurements 5 cm to 10 cm below the water surface and is capable of very accurate depth control (1cm) allowing for high vertical resolution observations within the very near-surface. We describe the integrated system and its characterization and calibration. Initial measurements and results from observations of coral reefs in Kaneohe Bay, Oahu, extremely turbid waters in the Chesapeake Bay, Maryland, and in Case 1 waters off Southern Oahu, Hawaii are presented., , ,